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These numbers were taken from the latest O/H manual dated 1984, but after looking again, I'm suspicious of the O-200 numbers. They indicate the early model 35' degree overlap, instead of the 24' degree model.

I wonder if.....

I wonder if the higher overlap camshaft could be legally used on ANY 0-200? Using this camshaft would effectively move the peak torque to a much lower rpm, where you could use the power, not at 2700rpm, where you would almost never see? The real advantage of the C90 over the 0-200 is that it makes much more power at a lower (usable) rpm.

So I wonder if anyone can confirm with certainty what the O200 camshaft specs actually are?

Originally Posted by Nathan K. Hammond

I think you're right.

These numbers were taken from the latest O/H manual dated 1984, but after looking again, I'm suspicious of the O-200 numbers. They indicate the early model 35' degree overlap, instead of the 24' degree model.

0-200 camshaft

According to my degree wheel and math the 0-200 cam using the opening and closing numbers posted is 259 degrees duration on both intake and exhaust with lobes centered @ 107.5.degrees.

Jerry is correct in that cam measuring specs can be given in a couple different ways.Measurements are sometimes given at a certain amount of tappet or valve lift,say .050".

There is a lot to camshafting,more than just a few numbers.Lobe profile is one.A cam lobe has a point where it begins to lift,a peak and a closing point but the ramp profile in between can have many variations.

An example would be in Stock class racing.The lobe must meet the factory opening and closing and max lift spec but the ramps between can be much more aggressive.This opens the valves at a quicker rate and delays the closing in the same way.The lobe profile looks nothing like a stock cam but when degreed it will check to the same spec.Very hard on valve springs but huge power !

There is no doubt in my mind that a better cam,not a radical one but a better one would really wake these little engines up.Try talking to Continental about it if your up for an exercise in frustration.They were not even willing to give specs to me ,told me it was proprietary info.I asked if they knew what a degree wheel and dial indicator were used for.

Is there any after market cam manufacturer, or builder, doing any development work on cam profiles for either continental or lycoming 4bangers? In these day of cad/cam I would think someone would be working on it.

0-200 camshaft

Lycon could probably tell you if anyone is currently doing other than stock cam profiles.

Any cam manufacturer has the ability to run a theoretical profile and grind it.Having a core with enough material to allow for a profile change would likely be a problem.Making a complete cam from a billet would be the only way to do it in that case.

Increasing rocker arm ratio is another way to gain a little cylinder filling without getting into the case.There are things like valve to piston clearance,spring coil bind,pushrod tube space,rocker stand strength,rocker cover clearance,just to point out things that must be considered.

What I would do is look for more torque.Intake tube length and volume are variables that can greatly affect the torque output and curve.
This is the same as the tuned exhaust principle.

The intake and exhaust flow moves to and fro in the pipes in a pulsing manner.Think of it like a slinky.What you want to achieve is to get the flow in a rhythm with the valve timing so it fills the cylinder with as much fresh fuel and air as possible in the time allowed by the open valve.Tube size and length affect velocity and that affects time and the timing of the pulse cycle.

Some times a length change of 1/4-1/2 inch can make a noticeable change.I have used a 2" spacer under a carb to change the length of the whole system.Different size spacers where the intake flange meets the cylinder would be easy to fabricate.Install some long studs and try some different ones.Longer tubes could be made quite easily.Remember tube size/volume and length go hand in hand.

Lots of these engines do not have equal length runners either.This is mostly done for cost and ease of manufacture.

A good source for this type of stuff is Society of Automotive Engineers website.

Hope I didn't bore anyone.I love this stuff.Finding more power has always been fun. Bill

With all the pylon racers in that one class running those O-200s, none of them must have a cub. Ive never seen any chime in here. I know its a different game they play with the high rpm,s and style of aircraft. But theyed be the ones that would know what would keep a 200 purring or not. Anyone familiar with any of those guys. doug

0-200 camshaft

Boring the intake pocket to install the big valve probably leaves too little material.Small block chevy did the same with 2.02 valve

Something in human nature says bigger is better.Winston Cup engine builders learned that an intake manifold with bores SMALLER than the restrictor plate Nascar supplied actually flowed better because it kept the airflow in the center of the carb bore and away from the protruding restrictor plate.

The cylinder head design of these aircraft engines is junk.Right angle port entry and exit is about as bad as youcan get.An 0-200 has a round intake tube to a 90 degree elbow to a rectangular port to a round valve.Take a piece of u-channel and lay that out and try to flow water through it.
Air has mass and it does not like sharp bends,and shape changes.All the same things an airfoil is subject to apply here.
A straight forward thing like cyl castings with a better port angle would give tremendous gains.

Volumetric efficiency is the term that applies here.
Oh and don't bother trying to polish intake spiders,tubes or ports.A better finish is sandblasted or like a 36 grit paper would leave.The smooth polished surface promotes fuel puddling.Rough shreds the fuel droplets promoting better exposure to the oxygen resulting in more complete combustion.
Cars, motorcycles,jet skis,airplanes,they all respond to physics.

Yeah, I make my living doing fluid mechanics. I agree. My hunch is that with an appropriately designed spider, intake elbow and intake port, the O-200 would do better with a smaller intake valve -- but, with the present design, I suspect a larger valve that opens faster might do better than the stock valve. For esthetic reasons on J3's, I wouldn't want to change the external appearance too much. I do like to rework the interior of the spider, but do not polish it.
JimC

0-200 camshaft

OK here it is right from Continental.I got a guy that really wanted to help.

The numbers posted above as far as opening and closing points are correct.

The C-90 and 0-200 both are.410"lift cams.

The C-90 is 245 degree duration on both Intake and Exhaust with a 24 degree overlap.

The 0-200 is 259 degree duration on both Intake and Exhaust with a 35 degree overlap.

The C-90 cam will produce it's peak torque at a lower rpm due to it's shorter duration and overlap.

The 0-200 cam will produce more power up top.That said ,there is no reason to run the C-90 cam in an 0-200 UNLESS you are limited to the rpm you are allowed to turn by STC .

Continental built the 0-200 for the Cessna 150.it did not have the ground clearance to run a 74" prop like a Cub or other tailwheel aircraft.The only way to get the needed thrust with a short prop was to cam it so it could be spun higher.

My 0-200 turns 2600 with the brakes locked.I cruise 2550@5gph leaned and see 92 mph.That is with a 75-35 prop.I think the 75-38 would be perfect.And a 0 thrustline works as well on an 0-200/cub as it does on a Supercub! Hope this answers your question. Bill

0-200 camshaft

I spoke to Don Swords this morning.The specs Continental gave me were for the 176 cam.Don said they won't give the 788 specs.He did not have the specs in front of him but did say the 788 has 35 degrees of overlap and the opening and closing specs are different from the 176.

I also spoke to Competition Cams about doing a regrind and they said it usually runs about $ 125.They would need a core and the specs you wanted or they could develop a profile. Bill

Still no numbers for the 788 cam. I have a new one at home on the shelf. When I get home in the fall, will take it to the cam shop and have them run a profile. If anyone wants one, can have them run sum at that time.

O-200 Camshaft

Maybe somebody can help to find my peace after a lot of years, asking hundreds of so called experts and after paying 12k$.......
years ago I rebuild my 2nd PA-18 with a O-200, 0h, freshly overhauled in the US and shipped to Germany. It was mounted in and right the 1st test run showed an abnormality, at full throttle 2100 RPM the engine was running rough and was shaking & stuttering. When I pulled the mixture a little bit it ran smooth and ground RPM was about 2150 with temps in the green arc. Changed Carburetors with different settings, Propellers with different pitch, checked the Primer pump, the gap in the air box, fuel flow, valve springs, mag's etc. nothing at all...............
I contacted the deliverer in the US, with a few words, the 2 brothers at E........ton refused the warranty. I flew the PA-18 for some 150h and finally I had to take off the engine, replace the 2 burned cylinders and it was converted to a C-90-14F and it ran fine after.
I never found out the reason of that symptom, not even the shop who did the conversion could explain that. My thought was, that there was mounted a wrong camshaft as for an engine for industrial use or similar. even if the Camshaft showed the right P/N according the Overhaul manual. Now, after years, reading about the valve overlapping due to a wrong Camshaft.... this could be the reason why!
Had somebody had same or similar problems????

1st time was rebuild in the US, a shop at Elisabethon and 2nd time near Frankfort/Germany.
The C-90-12F of my 7-EC and the O-320 PA-12 were rebuild by Ole Joergensen, Padborg/Denmark, never had any problem with them

O-200....full throttle....2100rpm?
I'll bet if I had a prop on my O-200 that only let it turn 2100rpm static that it would be very unhappy.....
I would suspect that the C90 cam would be happier at that static rpm (but it still seems pretty low ...)
DaveG